Head motion is a common problem in functional MRI (fMRI) experiments, particularly in studies involving injections of drugs. A voluntary head-motion suppression method using the feedback to subjects on their own head motion information in real time is proposed. A real-time fMRI system was developed on standard MR imaging hardware for this purpose. The feedback of head motion information was simplified as a four-way arrow group changing color from green to red when a composite online head motion index went beyond a pre-specified threshold. The arrow indicators were programmed in E-Prime in order that the feedback of head motion information could be integrated into the commonly used visual verbal N-BACK task. A significant suppression of head motion was obtained consistently on all the subjects while the influence on the performance of task and the interference to brain activation had decreased to a minimal level. This method has been routinely used for quality assurance and reduction of head movement in our fMRI experiments.